Middle Muffler or No Middle Muffler?

I'm having a real problem finding the middle muffler (aka resonator) assembly for my 1976 300D (115 series)...other than from MBZ for $400!!!

I've been told by a local muffler shop that I really don't need the resonator, and that replacing it with just pipe will boost power slightly (any boost in power is welcome with the 300D)...they say the only downside is that it will be a bit noisier without the resonator.

On the other hand, the MB dealership tells me that the engine could be adversely affected without the resonator...that "your car was designed to have a resonator for a good reason."

So, should I replace the resonator assembly with pipe. or will this have some detrimental affect on the engine?

Robert